1. Field of the Invention
The present invention relates to a household electric appliance equipped with a piezoelectric pump and more particularly relates to a household electric appliance in which the piezoelectric actuator is electrically powered by the mains voltage without using an isolation transformer.
2. Description of Related Art
European patent #610 569 discloses a clothing iron having a piezoelectric pump for supplying a vaporization chamber with water from a storage vessel. This document describes the presence of a layer of electrically insulating material on the surface of the metal membrane in contact with the water in the pumping chamber. Such a document, however, does not describe the nature of the electrically insulating material applied to the metal membrane.
The application of a layer of insulating material to the metal membrane has the disadvantage of reducing the performance of the pump by limiting the vibration amplitude of the membrane. This problem becomes even more significant when the excitation voltage of the piezoelectric actuator is relatively weak, for example less than 120 V, which is in particular the case when the pump is powered by the domestic mains voltage in certain countries such as the USA. Furthermore, the standards in effect in certain countries, in particular the UL standards in the USA, impose additional constraints on the construction of the piezoelectric pump.
As a consequence, the selection of an insulating material to apply to the metal membrane poses a significant technical problem for the skilled professional.
An object of the present invention is therefore to propose a household electric appliance having a piezoelectric pump powered by the domestic mains voltage, without the interposition of an isolation transformer, which is capable of operating with a satisfactory output in most countries, particularly in the USA where the supply voltage is weak and where the appliance must comply with UL safety standards.